# CVE-2026-59933: PhpSpreadsheet: XLS/OLE sector-chain self-loop causes memory exhaustion > Attackers can cause memory exhaustion and denial of service by uploading a small malformed XLS file to applications using PhpSpreadsheet. - **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 28 Jul 2026 - **Updated:** 28 Jul 2026 - **Also known as:** GHSA-xh5m-36r6-47m3 ## What is CVE-2026-59933? CVE-2026-59933 is a high-severity denial of service vulnerability in PHPOffice PhpSpreadsheet, published on 28 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. ### Official description PhpSpreadsheet is a pure PHP library for reading and writing spreadsheet files. In versions 4.0.0 through 5.8.0, 3.3.0 through 3.10.6, 2.2.0 through 2.4.6, 2.0.0 through 2.1.17, and all releases up to and including 1.30.5, the OLE reader follows sector chains from attacker-controlled XLS/OLE metadata without detecting cycles or enforcing a maximum chain length. A tiny malformed .xls/OLE file can set the small-block depot sector chain to point back to itself. During normal XLS detection, OLERead::read() appends the same sector data repeatedly until the PHP process exhausts memory. This is reachable from Reader\Xls::canRead() and therefore from automatic spreadsheet type detection. Applications that accept attacker-controlled spreadsheet uploads can suffer denial of service from a very small file. This issue has been fixed in versions 5.8.1, 3.10.7, 2.4.7, 2.1.18 and 1.30.6. Weakness: CWE-835 (Loop with Unreachable Exit Condition), CWE-400 (Uncontrolled Resource Consumption) ## Which versions are affected by CVE-2026-59933? 10 open source packages ship an affected version, including phpoffice/phpspreadsheet. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `phpoffice/phpspreadsheet` | Packagist | All versions | 1.30.6 | | `phpoffice/phpspreadsheet` | Packagist | All versions | 1.30.6 | | `phpoffice/phpspreadsheet` | Packagist | From 2.0.0 | 2.1.18 | | `phpoffice/phpspreadsheet` | Packagist | From 2.0.0 | 2.1.18 | | `phpoffice/phpspreadsheet` | Packagist | From 2.2.0 | 2.4.7 | | `phpoffice/phpspreadsheet` | Packagist | From 2.2.0 | 2.4.7 | | `phpoffice/phpspreadsheet` | Packagist | From 3.3.0 | 3.10.7 | | `phpoffice/phpspreadsheet` | Packagist | From 3.3.0 | 3.10.7 | | `phpoffice/phpspreadsheet` | Packagist | From 4.0.0 | 5.8.1 | | `phpoffice/phpspreadsheet` | Packagist | From 4.0.0 | 5.8.1 | ## How do I fix CVE-2026-59933? Upgrade phpoffice/phpspreadsheet to a fixed version for your release line: 1.30.6, 2.1.18, 2.4.7 or 3.10.7. ## Is CVE-2026-59933 being exploited? It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-59933 exists. ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-59933 and fix it if it is affected. What it is: CVE-2026-59933 is a high-severity denial of service vulnerability in PHPOffice PhpSpreadsheet, published on 28 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-59933 exists. Affected packages and fixed versions: - phpoffice/phpspreadsheet (Packagist): affected all versions; fixed in 1.30.6 - phpoffice/phpspreadsheet (Packagist): affected all versions; fixed in 1.30.6 - phpoffice/phpspreadsheet (Packagist): affected from 2.0.0; fixed in 2.1.18 - phpoffice/phpspreadsheet (Packagist): affected from 2.0.0; fixed in 2.1.18 - phpoffice/phpspreadsheet (Packagist): affected from 2.2.0; fixed in 2.4.7 - phpoffice/phpspreadsheet (Packagist): affected from 2.2.0; fixed in 2.4.7 - phpoffice/phpspreadsheet (Packagist): affected from 3.3.0; fixed in 3.10.7 - phpoffice/phpspreadsheet (Packagist): affected from 3.3.0; fixed in 3.10.7 - phpoffice/phpspreadsheet (Packagist): affected from 4.0.0; fixed in 5.8.1 - phpoffice/phpspreadsheet (Packagist): affected from 4.0.0; fixed in 5.8.1 Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2026-59933/ (Markdown: https://insights.sbomify.com/CVE-2026-59933/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-59933 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-59933 - OSV: https://osv.dev/vulnerability/CVE-2026-59933 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-59933/ Summaries are generated and may contain mistakes; the official description above is the record.